Hi David,

Try and get some benzoic acid and put that into the citric acid container. Benzioc acid will reduce/stop the growth if microorganisms. As Martin says, use a lightproof bottle.

Thor

Edited By Thor on 01/11/2013 17:44:44

I find that Tupperware gets infected with mould spores, the growth can be restricted, I'v got a large container in the kitchen for kitchen scraps, and it often gets furry.

Bleach in the acid would tend to neutralize the mixture. Forget the mould, it's doing no harm. Ian S C

Ian and Russell,
Doing no harm? What do you think the bugs live on? In the case of Sulph. acid, I bet its the Sulphur content, thus steadily weakening the acid strength. Suggest you scrape `em out and maybe dose bugs with aa strong alkali to neutralise before diposal. As you say, could ignore till acid knackerred and replace with fresh.
John.

Edited By DMB on 02/11/2013 11:46:14

A splash of household bleach, added when the mix is made, prevents any unwanted growth, at least , this has been my experience when using citric acid.

regards,

David.

Thinking again – what's all this with citric acid? If this is being used these days for pickling copper prior to silver soldering then it is a new one on me. Going back 30 years or so everyone seemed to be using dilute sulphuric acid – I know I did.

Fill me in someone please.

Rik

Is Citric acid available on the local market…where do you get it from, Chemists, garden centre's,.. liquid, powder form etc..? Interested for future ref.

George

Is sulphuric acid really more dangerous than citric.?

It has been stated that citric acid works slowly. This is because the solution is low in acidity (the PH is not very low). If you use a weak solution of sulphuric acid such that the PH is the same it will take equally long to work but should be no more dangerous than citric acid.

Sulphuric acid is available here (France) in all DIY stores and many supermarkets. It should be available in the UK as battery acid. I buy 30% strength and use it diluted 10:1 with water. It works in a few minutes. Dilute it more if you are worried about safety but always remember to add the acid to the water not the other way round.

Russell.

One Shot (?) drain cleaner is easily available from B&Q etc. and is something like 90% sulphuric acid. Make sure you get the one that is sulphuric acid based though. It's available from Ebay as well so must be able to post it!

I do use citric acid but still prefer sulphuric acid for copper.

John

As I said, it depends on the strength of the solution. A weak solution, less active and less dangerous.

You can buy battery acid ( about 35% w.w. sulphuric acid) by post. For example

Russell

Sulphuric acid has a pKa value over 6 below that of citric acid – which means it would have to be diluted enormously (somewhere between 10,000 and one million times) to have the same pH. It would become exhausted very rapidly at this concentration.

In practice, something around 10% should work fine – but be aware it can, even at this concentration, be very irritating to skin and damaging to eyes; it can also destroy fabric over time as it becomes concentrated through evaporation.

I have found sulphuric acid quite easy to buy from jewellers' suppliers – though you may need to sign a book stating the purpose for which you want it ("pickling" should be fine). It was a few years ago though, so it's possible things have changed. I honestly would not recommend anyone to buy/use concentrated sulphuric acid unless you know what you are doing – your point about *always* adding acid to water is bang on, but also bear in mind that so much heat is generated that the solution can boil. Either do it gradually with intervals to cool, or add acid to ice.

Citric acid is readily available through Amazon or eBay.

David

Edited By David Littlewood on 04/11/2013 19:36:55

SO2 isn't very odourless in these parts!

Neil